fibril (fīʹbrəl, fĭbʹrəl) noun. 1. A small, slender fiber or filament. 2. Anatomy. Any threadlike fiber or filament, such as a myofibril or neurofibril, that is a constituent of a cell or larger structure, fibril

fibrillation (fĭb´rə-lāʹshən, fī´brə-) noun. 1. The forming of fibers. 2. a. Fine, rapid twitching of individual muscle fibers with little or no movement of the muscle as a whole. b. Rapid, uncoordinated twitching movements that replace the normal rhythmic contraction of the heart and may cause a lack of circulation and pulse, pemfibrilatan; pemfibrilan